1. Technical Field
The present invention relates to the technology of electronic well logging. More particularly, the present invention relates to determining or identifying fluid means in a well bore using electronic logging instruments. Still more particularly, the present invention relates to a method and apparatus for identifying a fluid in a well bore using a slickline logging instrument.
2. Description of the Related Art
FIG. 1A is an illustration of a standard rig-up for performing down-hole logging operations in a well bore. Generally, logging is performed by a logging services truck 102. Although truck 102 typically contains a number of different features, for this application, truck 102 contains drum 104, which spools off cable 106 through a combination measuring device weight indicator 108, which will be described in more detail below. Cable 106 is rigged through lower sheave wheel 110 and upper sheave wheel 112, and enters the well bore through pressure control equipment 114, used to contain well bore pressure while allowing a cable to move freely in and out of the well bore. Cable 106 enters the well bore at well head connection 116, upon which pressure control equipment is connected. Below surface 118, pipe or casing 120 proceeds in a generally vertical direction to a bottom depth (not shown). Within casing 120 is logging tool 125, connected to cable 106. Casing 120 is a group of casing joints 121, generally 40 to 44 feet long, connected by casing collar 122 and cemented into place in a previously drilled bore hole.
One of the most important measurements provided by a logging truck is the depth measurement. Accurate depth measurements are essential in properly evaluating the well bore. Combination measuring device weight indicator 108 consists of at least one, but normally a plurality of measure wheels 130. The Advanced Measurement System for slickline is an example of such a device used by the Halliburton Company, 3600 Lincoln Plaza, 500 N. Akard St., Dallas, Tex. 75201. Measure wheels 130 are precision ground to a precise diameter, and turn proportionally with cable 106 as it goes into and out of the well bore. Measure wheels 130 are mechanically connected to a depth encoder device (not shown) that provides digital signals based on the position of the depth wheel. Thus, as cable 106 moves into and out of the hole, a plurality of depth signals are sent into the logging compartment of truck 102 in order to provide the operator with accurate digital depth data. Additionally, combination measuring device weight indicator 108 contains cable tension wheel 132. Cable tension wheel 132 applies a set amount of pressure against cable 106, in the direction of measure wheels 130. As the amount of cable in the well bore increases, the tension applied by the weight of the cable resists against cable tension wheel 132, causing the load on cable tension wheel 132 to increase toward measure wheels 130. Cable tension wheel 132 is mechanically connected to a load cell, and as the weight of cable 106 increases, causing the load on tension wheel 132 to increase, the load cell sends a signal into the logging compartment of truck 102, indicating an increase in the tension on cable 106.
Generally, down-hole or well logging can be divided into two categories: wireline logging, and slickline logging. Wireline logging allows for more sophisticated services and tools to be run in the well bore. Wireline cable is a braided cable which, at its center, contains one or more electrical conductors. These conductors pass electrical signals to and from logging tool 125, along with the power needed to operate the down hole components of logging tool 125. Conversely, a slickline may be a braided line but contains no electrical conductors. Therefore, services normally run by a slickline logging unit are generally mechanical in nature and usually do not transmit a signal up-hole, as slickline cable lacks any conductor means for transmitting electrical signals containing data information. However, there are exceptions.
The logging operation pictured in FIG. 1A is that of a collar locator. Logging tool 125 is divided into two sections. The first, collar locator 140, emits a magnetic field and detects the interference with the magnet field caused by a casing collars. A casing collar location signal is then transmitted from casing collar 140. The second section, lower electronic magnet/drag sub-assembly 142, responds to the casing collar location signal transmitted by casing collar 140 by instantaneously activating an electromagnet.
Normally, logging operations proceed as the logging tool moves in an up-hole direction. By logging in the up direction, accurate depth measurements can be maintained because the tension at logging tool 125 remains relatively constant, even though the tool may be scraping along the side of casing 120. Alternatively, if logging in the down-hole direction, logging tool 125 may intermittently drop and drag as it makes its way down casing 120. Because the only tension applied to logging tool 125 in the down-hole direction is due to gravity, or the weight of the logging tool itself, depth measurements in the down-hole logging direction tend to be far less accurate.
Note that cable 106 has a slight amount of slack in it between truck 102 and lower sheave wheel 110. Although not shown, the amount of tension from upper sheave wheel 112 to logging tool 125 also contains a certain amount of slack. The amount of slack varies from time to time due to logging tool 125 hanging up on the well bore in downhole logging operations, causing inaccurate depth measurement readings at the logging compartment. Conversely, the amount of slack between logging tool 125 and truck 102 (and in the well bore) remains relatively constant while logging in the up-hole direction, because cable tensions is driven by the cable winch at the logging truck rather than by gravity. Depth measurements are much more accurate. Therefore, the preferred method for logging is in the up-hole direction.
Another problem more commonly associated with slickline operations is the problem of line or cable stretch. While all cable stretch as tension is added to the cable, slickline cables are generally smaller in diameter and, therefore, the magnitude of the stretch is greater. Some combination depth measurement and cable tension measurement devices, such as the Advanced Measurement System for slickline used by the Halliburton Company, will correct for line stretch and other environmental factors that effect slickline measurements.
As can be seen in FIGS. 1A and 1B, logging tool 125 is moving in the upward direction, and lower electronic magnet/drag sub-assembly 142 is across collar 122. As can be seen in FIG. 1B, as logging tool 125 moves upward, and collar locator measure point 144 comes across the abutment of two joints of pipe within collar 122, collar locator 140 sends a casing collar location signal to lower electronic magnet/drag sub-assembly 142. At that point, magnets within electronic sub-assembly 142 are momentarily activated, and logging tool 125 momentarily sticks to the wall of casing 120. As logging tool 125 sticks to casing 120, tension is increased because the cable winch at logging truck 102 continues turning. An increase in cable tension is detected by combination measuring device weight indicator 108 and can be read on a panel inside logging truck 102.
FIG. 2 illustrates up-hole components that may be found in a typical logging unit, such as that shown in FIG. 1A. Combination cable tension speed device 200 represents a combination tension and speed readout display. Note that line tension is available to the operator in either analog form from cable tension dial 202 or in digital form from cable tension digital readout 204. In this case, the tension is approximately 1510 pounds. Cable tension dial 202 includes tension needle 205 and increment needle 206. Increment needle 206 is scaled at 10 percent of the reading of tension needle 205 or the current cable. In this case, full scale for increment needle 206 is scaled at 151 pounds. Thus, if the logging tool hangs up and tugs or pulls 151 pounds on the cable, the increment needle will move full scale, or to the 100 mark of the cable tension dial 202.
In practice, as a logging tool moves up-hole, if the tool starts to drag, the increment needle moves up at approximately ten times the travel of the weight indicator needle. Thus, the operator is given an immediate and accurate representation of any tugs or pulls, in many cases before an indication is registered on cable tension needle 206. Thus, the operator is given time to react before the tension on the tool head becomes critical.
Also provided on combination tension cable speed device 200 is speed dial 210 and speed digital readout 212, which indicate the speed at which the cable is traveling into or out of the well bore. The cable speed readout gives the operator an accurate cable speed indication for logging operations, as well as a reliable method for gauging logging tool float as the logging tool is lowered into the well bore.
Conventional slickline trucks that only perform mechanical services may only be equipped with a combination line tension cable speed indicator and a depth indicator. However, recent advancements in well logging technology have allowed for the placement of low-cost portable well log computers, such as that shown in FIG. 2. One example is the Slickline Data/Job Logger used by the Halliburton Company. Logging computer 250 contains digital display 252, a number of manual dials 254, and a series of buttons 256, along with a depth-set thumb wheel 258, and a depth-set button 260. Buttons 256 can be used to control data for display on logging computer 250. In general, they include a means for indicating logging sequence (either up or down) and for calibrating the tool or depth equipment, a means to save, and a means to print a representation of the data, normally called a log or an electric log.
The representation of logging computer 250 in display 252 includes a three-track linear logging grid generally referred to as a log. The log consists of one linear grid track on the left, a depth track for displaying depth numbers, such as 1700 and 1800, without grid, and two linear grid tracks on the right. In this particular model, display 252 is a touch panel, allowing for a plurality of buttons to be displayed for configuring the display of the electric log. Typical functions might include a menu function, an input function for identifying the input to the device, a trace output function, along with trace coding and scaling functions for identifying the individual traces in the tracks and coding and scaling the traces, along with a depth scale for identifying how many feet per inch will be displayed on display 252. In this particular example, traces 270 and 262 are shown on the display. Trace 270 is a tension trace of tension received from combination tension cable speed device 200. Note that, at certain intervals, the tension device spikes higher, as shown, for example, at points labeled 264. These points correspond with casing collars 122 in casing 120 from the previous illustration.
Also shown on the log is an example of a wireline casing collar locator 262. It should be understood that rarely, in practice, would a wireline casing collar trace be overlaid on a log generated with a slickline collar locator trace. The present example is provided in order to give a better understanding of the operation of the slickline logging operation. Trace 262 depicts a tracing collar locator log as received from a wireline casing collar locator. Note that the collars are identified by lateral variations of the casing collar locator signal, which culminates in a high magnitude deviation from the base point, indicating a casing collar. These are shown at points 266 on trace 262 and identify the location of casing collars. Note that casing collar locators, identified on the electric log as points 266, correlate perfectly to casing collars 264 on casing collar locator trace 270, as input from this slickline log.
As can be seen in the example, the slickline logging operation that uses a collar locator in combination with a lower magnet/drag sub-assembly provides casing collar identification and depth measurements comparable to the more expensive wireline logging operation. Thus, even though slickline logging operations do not have the means to transmit electrical signals including data information up-hole in real time, the information can instead be transmitted in real time up-hole using the line tension on combination measuring device weight indicator 108. In so doing, a slickline operator can provide the same information as an electric operator, at a fraction of the cost of using an electric line.
FIG. 3 is a chart illustrating a down-hole logging service of fluid depth determination performed by both slickline and wireline. In FIG. 3, well bores 310, 320 and 330 illustrate the same well bore but show different down-hole logging tools. Although well bores 310, 320 and 330 are disclosed as casing lined, the down-hole logging tools described below may be used in either casing or production tubing for detecting fluid and identifying fluid types. Well bore 310 contains slickline tool 312. Generally, when attempting to identify a fluid level in a well bore using slickline, either a gauge cutter or a blind box is configured at the bottom of slickline tool 312. The gauge cutter resembles a biscuit cutter on the bottom, is hollow in the center with fluid bypasses cut above the cutter, and contains a threaded top end to attach it to the bottom of a slickline tool string. The blind box is a solid piece of steel with a flat smooth bottom and a threaded top end similar to the gauge cutter. The blind box is the preferred tool for locating fluid levels, as it has no fluid bypass through its center.
Blind box 316 is attached to the bottom of slickline tool 312 and run in the hole on slickline at a constant, fairly high rate of speed, approximately 100-200 ft/min. When a fluid level is encountered, a reduction in line speed and loss of weight occurs due to fluid bypass restriction of fluid flow around the tool. When pulling out of the hole at a constant speed, a loss of weight indicates that the tools have been pulled out of a fluid level. As blind box 316 contacts the fluid level in the well bore, the change in cable tension registers on the cable tension display as described above. In the configuration shown in well bore 310, as the cable moves downward and blind box 316 contacts fluid, the logging tool is held up slightly, and the slickline operator can note the top of the fluid column from the weight indicator reading.
Well bores 310, 320 and 330 contain four distinct zones. Zone 301 is the air zone on top of the fluid column. Zone 302 is the lightest fluid contained within the well bore. In this case, it is a combination of oil and soluble gas. Soluble gas makes the oil much less dense than the density of oil, and often a zone of soluble gas and oil form over an oil zone in a well bore. Zone 303 is a column of oil that is separated from zone 302, which contains the soluble gas. Note at the bottom of zone 303 a series of perforations 350, which allow for the communication of the fluids within the well bore to the formation. Normally, perforations such as those shown in the depicted example are made for producing oil in a formation reservoir. A perforating gun is lowered to the desired depth, and the gun is discharged, firing a plurality of shape charges, which penetrate the wall of the casing and the cement behind the casing.
In the depicted example, well bores 310, 320 and 330 have a sump, which is that portion of the well bore below the bottom perforation, in this case, zone 304. Normally, the sump contains a reservoir or formation water, but it also may contain contaminated well bore drilling fluids, such as mud and other debris. Typically, in a producing well, or even in an injection well, the sump will contain reservoir water, which is usually saline water of somewhat higher density than fresh water. While using slickline logging tool 312 may provide valuable information as to the top of the fluid column in the well bore, slickline logging tool 312 has problems identifying fluid types and, in many instances, has problems identifying the exact depth of even the fluid column itself.
Well bore log 360 shows a plurality of traces, including tension trace 318, which might be expected from a slickline operation for determining a fluid column using a blind box, as shown in the depicted example. Notice the tool travels downward in well bore 310. Tension trace 318 stays relatively straight and maintains a gradient related to the additional weight of the cable going in the hole. In this case, the fluid level is at approximately 1785 feet, as indicated at point 345. Note that, as tension trace 318 crosses the interface between zone 301 and zone 302, the tension trace remains relatively stable for approximately six feet. At that depth, approximately 1791 feet, the tension gradually reduces until, at approximately 1800 feet, tension trace 318 again stabilizes and again remains relatively flat for a number of feet. Note at a depth of about 1870 feet, at point 319, the tension trace is again reduced momentarily through the interval of about eight feet. Still further down, at the interface of zone 302 and zone 303, tension trace 318 once again is slightly reduced at point 321, for an interval of about ten or twelve feet.
At first appearance of trace 318, an operator might wrongly conclude that three separate fluid types have been detected: one at point 317, one at point 319, and one at point 321. Careful examination by an experienced well logger would reveal that point 317 is indeed a contact with a fluid top. However, note that even the highest reading of point 317 is about six feet off the mark of the fluid top in well bore 310. Note also that, at point 319, where tension trace 318 momentarily lags or reduces, the entire tension comes back. While this could indicate a fluid level, it could also indicate debris in the hole being pushed down by slickline tool 312.
More difficult to detect, at point 321, is another reduction in tension trace 318. While this point roughly correlates to the interface between zones 302 and 303, by comparing tension trace 318 to collar locator trace 362, it is apparent that what has actually happened is, blind box 316 has hung up on a casing collar directly above point 328. Once sufficient cable slack was spooled into the hole, slickline tool 312 fell past collar 361, and tension trace 318 resumed its normal down-hole gradient.
Well bore 320 shows the identical well bore, but this time containing wireline logging tool 322. Wireline logging tool 322 is a combination of the collar locator and the fluid density measuring device, sometimes known as gradio-monometer 326. Gradio-monometer 326 uses a plurality of pressure sensors for determining an exact fluid density. On collar locator 324 is the measure point 323, used for identifying the depth of the casing collars. Unlike slickline tool 312, wireline tool 322 would normally log in the up-hole direction and produce fluid density trace 350. Note that fluid density trace 350 contains three separate fluid density changes. The first is at point 325, where the tool moves from the top fluid to air (zone 301 to 302). In this case, the density of the top fluid is approximately 0.70 to 0.75 gm/cc, and the air dropped down to around zero. This correlates exactly to the interface between zones 301 and 302.
Further down, at the interface between zones 302 and 303, is another point, point 327. Fluid density trace 350 shows a density change from approximately 0.80 or 0.85 gm/cc to 0.70 to 0.75 gm/cc. In this case, the density of the crude oil of zone 303 is approximately 0.80 to 0.85 gm/cc. Note also that wireline logging tool 322 has detected the exact point at which zone 302 interfaces zone 303, unlike the slickline logging tool.
Finally, fluid density trace 350 shows the exact interface between zones 303 and 304, precisely at the bottom of the perforations, as would be expected. Note also that, at that point, the density changes from that of crude, around 0.80 to 0.85 gm/cc, to that of salt water or contaminated salt water, just over 1.0 gm/cc, roughly 1.05 gm/cc in the depicted example. As can be seen, wireline gradio-monometer 326 provides much better fluid identification information; but also, it provides more accurate depth information because, one, the tool logs in the up-hole direction and, two, the tool responds to only fluid densities or changes in fluid density, unlike blind box 316 on slickline logging tool 312, which responds to the fluid tops but also responds to junk or debris in the hole, deformed hole and casing collar locators, and also perforations or other protrusions, which may hang up blind box 316 on its travel down the hole.
Well bore 330 depicts an alternative to using gradio-monometer 326. Wireline logging tool 340 is similar to that described immediately above, in that it contains casing collar locator 322 with measure point 323. However, rather than using gradio-monometer 326, wireline logging tool 340 uses a radioactive or nuclear type fluid density sensor. It is well known to obtain the approximate density of rock and fluids by bombarding the fluid or rock with radiation and using a radiation detector measuring the amount of radiation that is allowed to pass through either the fluid or matrix rock. One means uses a gamma ray source, such as cesium, radium or cobalt, and one or two gamma ray electors, which measure the amount of gamma ray particles that find their way through the fluid to the gamma ray detector. The fluid density differential pressure tool (densometer) is one example of such a tool used by the Halliburton Company.
In another embodiment, a neutron source could be provided, such as americium-beryllium, and the radiation detectors would then detect the number of free neutrons that pass through the fluid and strike the detector. Function formers are used to calculate the number of counts per second perceived by one or both detectors in a given fluid type, and in a given fluid type of a given density. Using wireline logging tool 340, not only an accurate measurement of the density can be determined; but also, in many cases, the fluid type in the well bore can also be determined with certainty.
Fluid density trace 333 in track three of log 360 is produced by a radioactive fluid density tool. Note that, in zone 301, fluid density trace 333 exhibits a certain amount of random activity, as expected with a radioactive source logging tool. At the interface of zone 301 and zone 302, the density immediately proceeds to show an oil and gas density of around 0.70 to 0.75 gm/cc, similar to that measured by the gradio-monometer. Note also that, at point 335, the depth of the fluid top is determined exactly, unlike the fluid top that is determined by slickline tool 312. At point 337, fluid density trace 333 indicates a change in density from approximately 0.70 to 0.75 gm/cc to approximately 0.80 to 0.85 gm/cc. Note also that the depth of point 337 corresponds to the depth at which zone 302 interfaces with zone 303. Finally, at point 339, fluid density trace 333 detects an increase in fluid density from approximately 0.80 to 0.85 gm/cc to approximately 1.00 to 1.05 gm/cc, indicating that the tool has passed from zone 303, containing crude oil and the sump, to zone 304, containing contaminated well water fluids including formation water.
Alternatively, a capacitance tool, which indirectly relates the capacitance of a fluid to its specific gravity, may be used to identify fluids and fluid levels. This tool is used primarily to distinguish if a fluid is an oil or water. This tool is normally run in conjunction with a fluid density differential pressure tool, which utilizes a source to determine if a fluid is a gas or liquid. When used in conjunction with each other, these tools can determine gas, oil, and water contacts. In fact, most production logging operations employ a number of tools in combination in order to provide the well operator with a definitive answer as to fluid type or phase, and fluid contact levels.
As can be seen, accurate fluid levels can be determined by any number of tools in a wireline operation. However, fluid level determination using wireline is expensive. Generally, mechanical services, such as identifying fluid tops and gauging holes, have relatively low priority in the well life and, therefore, very little funds are allocated for these services. Slickline operations partially meet the needs of the well operators; however, the accuracy and limitations of the tools are suspect. While well operators may be getting some information, they may not be getting all of the necessary information; and some of the information may be inaccurate.
Therefore, it would be advantageous to provide a slickline operation for determining accurate fluid level depths. It would be further advantageous to provide a tool for identifying multiple intervals on a slickline. It would be even more advantageous to provide a down-hole tool for use in slickline operations which obtains real-time fluid identifications in multi-fluid well bores.